Fill and pressurizing system

ABSTRACT

A hydraulic booster is disclosed in which a generally cylindrical housing is divided by a separator into a reservoir chamber above the separator and an air motor cylinder below the separator. A differential area air piston located in the air cylinder drives a plunger along a hydraulic cylinder extending axially within the reservoir. Compressed air supplied to the reservoir causes hydraulic fluid to flow into the hydraulic cylinder pressurizing the system to a pressure approaching the air pressure. Valved means subsequently open to operate the air driven piston to further pressurize the hydraulic fluid within the hydraulic cylinder to the high required pressure.

nited States Patent [191 Seidel cti,i974

[ FllLlL AND PRESSURIZING SYSTEM Inventor: Lawrence H. Seidel,Cleveland,

Ohio

Assignee: .lergens, inc, Cleveland, Ohio Filed: Dec. 3, 1973 Appl. No.:420,762

Related US. Application Data Continuation of Ser. No. l58,429. June 30,l97l U.S. Cl 60/547, 60/574, 60/593 Int. Cl. F15b 7/00 Field of Search60/547, 560, 574, 576,

References Cited UNITED STATES PATENTS Primary Examiner-lrwin C. CohenAssistant Examiner-A. M. Z apcic Attorney, Agent, or FirmMcNenny,Farrington, Pearne & Gordon [5 7] ABSTRACT A hydraulic booster isdisclosed in which a generally cylindrical housing is divided by aseparator into a reservoir chamber above the separator and an air motorcylinder below the separator. A differential area air piston located inthe air cylinder drives a plunger along a hydraulic cylinder extendingaxially within the reservoir. Compressed air supplied to the reservoircauses hydraulic fluid to flow into the hydraulic cylinder pressurizingthe system to a pressure approaching the air pressure. Valved meanssubsequently open to operate the air driven piston to further pressurizethe hydraulic fluid within the hydraulic cylinder to the high requiredpressure.

13 Claims, 5 Drawing Figures 747 12/1948 Fischer et al. 60/547 ,76612/1954 Hufford 60/560 .l60 4/l960 Van Wart et al.. v. 188/357 1.792ll/l970 Ellis 60/534 PMENIED 8W4 3.839.866

SHEU 1 BF 2 INVENTOR.

4 Ala/196M676 56/054 PATENIEU 3W4 3.839.866

SHEEI 20? 2 /0/ l we 86 /03 l A 1 FILL AND PRESSURIZING SYSTEM This is acontinuation, of application Ser. No. 158,429 filed June 30, 1971.

BACKGROUND OF THE INVENTION PRIOR ART It is often desirable to userelatively low pressure compressed air, which is available in manymanufacturing plants or the like, to power a relatively high pressurehydraulic system. In such instances pressure boosters are often used,which employ differential area of piston means, so that the hydraulicoutput pressure substantially exceeds the compressed air pressureavailable to power the device. Examples of such devices are illustratedin the US. Pat. Nos. 2,877,624 and 3,473,328, the latter of which isassigned to the assignee of the present invention.

In both of these patents, hydraulic booster systems are illustrated forsupplying relatively high pressure hydraulic fluid to work clampingdevices or the like. Further, in both of these systems, a reservoir isprovided which contains hydraulic fluid and provides an air spacethereabove..Compressed air supplied to such reservoirs pressurizes thehydraulic fluid before the differential area piston is operated. Thehydraulic fluid, which is directly pressurized by the compressed air,flows to the clamping device to take up any clearances and to cause theclamping devices to be operated to a preliminary clamping condition onthe work piece. After the preliminary clamping is completed and thepressure builds up, the differential piston operates to increase thepressure of the hydraulic fluid supplied to the clamping device to thedesired high pressure.

SUMMARY OF THE INVENTION In the illustrated embodiment of the presentinvention, a simple structure is utilized in which valved means connectthe air chamber of the air motor portion of the differential area pistonto the air space within the reservoir only after the pressure in thehydraulic chamber portion of the pump reaches a predetermined pressureto insure that the air motor will not be actuated until the pressure ofthe hydraulic fluid supplied to the system approaches the pressure ofthe compressed air supplied. Such valved means then functions to connectthe air space in the reservoir to the air chamber of the air motor tocause the piston to further pressurize the hydraulic fluid. A simpleball valve element is actuated by a plunger exposed to hydraulicpressure to create this operation. The plunger of the differential airmotor which pressurizes the hydraulic fluid in response to operation ofthe air motor operates to automatically isolate the reservoir and thepumping chamber as soon as the plunger commences to move under theinfluence of compressed air.

The various components of this system are arranged so that substantiallyall of the hydraulic fluid in the system is available for the operationof the clamping devices. The illustrated system provides structuralintegrity, high reliability, low maintenance, and low initialmanufacturing costs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevation partiallyin section illustrating a pressure booster in accordance with thepreferred embodiment of this invention;

FIG. 2 is an enlarged fragmentary section of the valved systemillustrating the structural detail thereof;

FIG. 3 is a schematic illustration of the booster system illustratingthe position the elements assume prior to pressurization;

FIG. 4 is a schematic illustration similar to FIG. 3 but illustratingthe system after pressurization has commenced;

FIG. 5 is a schematic illustration similar to FIGS. 3 and 4 illustratingthe elements of the booster while the booster is being exhausted.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a booster inaccordance with the preferred embodiment hereof. Such booster includes abase 10, a head 11, and a divider or separator 12. A tubular member 13extends between the base 10 and separator 12 and cooperates therewith todefine the cylinder of an air motor portion of the device. Draw bolts 14extend between the base 10 and the separator member 12 and cause theends of the tubular member 13 to tightly engage radial surfaces 16 and17 formed on the separator 12 and base 10, respectively. O-ring typeseals 18 and 19 are provided on the base 10 and separator 12 to providea fluid tight joint with the inside diameter of the tubular member 13.

A second tubular member 21 extends between the separator member 12 andthe head 11. Here again, draw bolts 22 clamp the ends of the tubularmember 21 against radial surfaces 23 and 24 formed on the separatormember 12 and head 11. Seals 26 and 27 are engaged by the ends of thetubular member 21 to provide a fluid tight joint between the tubularmember 21 and the head 11 and separator member 12, respectively. Thetubular member 21 is preferably formed of a transparent material toprovide a visual indication of the level of liquid therein.

A hydraulic cylinder member 28 is threaded at its lower end into theseparator member 12 and extends at its upper end through a centralopening 29 in the head 1 l. A hydraulic cylinder bore 31 is formed inthe cylinder member 28 which extends to an outlet port 32 at its upperend. A sea] 33 is located at the lower end of the cylinder member 28 toprovide a fluid tightjoint between the cylinder member 28 and theseparator 12 and a pair of spaced seals 34 and 36 provide a fluid tightjoint between the upper end of the cylinder mem' ber 28 and the head 11at two spaced locations. A reservoir chamber 37 is defined by thecooperating separator 12, head 11, and tubular member 21 around thecylinder member 28. The lower portion of the reservoir chamber 37 isadapted to be filled with hydraulic fluid and the upper portion abovethe hydraulic fluid is an air space adapted to be pressurized withcompressed air. Normally, compressed air is used to power the device.However, other compressed gases may be used, and the phrase compressedair or the term air is intended to include other compressed gas orgases.

A differential area piston assembly includes a piston head 41 and aplunger 42. The piston head 41 is sized to extend to the inner wall ofthe tubular member 13 and divides the air motor portion of the deviceinto a lower air chamber 43 and an upper air chamber 44. A seal 46prevents leakage past the piston head 41. The plunger 42 which is drivenby the piston head extends through a seal 47 in the separator member 12and into a hydraulic pumping chamber 48 defined by the cylinder bore 31and an extension thereof 49 formed in the separator member 12 below theseal 33. An inclined passage 51 connects the lower end of the reservoirchamber 37 and the extension 49. The various elements are proportionedso that fluid communication is provided between the liquid portion ofthe reservoir chamber 37 and the hydraulic pump chamber 48 when thepiston is in the retracted position illustrated in FIG. 1, but also sothat as the plunger is moved upward, the upper end engages the seal 33to isolate the pump chamber 48 from the reservoir after the plunger 42engages the seal 33.

The head 11 is provided with an inlet port 52 through which compressedair may be supplied to or exhausted from the upper portion of compressedair space of the reservoir chamber 37. Similarly, the separator member12 is provided with a port 53 through which compressed air may besupplied to or exhausted from the chamber 44 of the air motor. These twoports are connected to a four-way valve 54 (illustrated in FIG. 4) whichcan be operated to selectively connect the reservoir chamber 37 or theair motor chamber 44 to a source of compressed air such as a compressorschematically illustrated at 56. The valve is arranged so that when thereservoir chamber 37 is pressurized, the air motor chamber 44 isexhausted through an exhaust 57. Operation of the four-way valve 54 tothe other position pressurizes the air motor chamber 44 while exhaustingthe reservoir chamber 37.

Mounted in the head 11 is a valve assembly 61 which controls theoperation of the differential piston. This valve assembly includes apressure operated valve and a back check valve 62. These valves bothcommunicate with a passage 63 which is connected through a pressure line64 to the lower chamber 43 of the air motor. Both of the valves alsocommunicate with the upper side or air space portion of the reservoirchamber 37 through a passage 66. Referring to FIG. 2, the back checkvalve 62 includes a valve body 67 held in a valve bore 68 by a capmember 69. Seals 71 and 72 prevent leakage along the bore past the valvebody 67 and cap 69, respectively. The valve body 67 is provided with acentral bore 73 open to the passage 63 and provides a valve seat 74 atits inner end. A valve disc 76 is normally seated against the valve seat74 by a spring 77. Communication between the spring side of the valvedisc 76 and the air space portion of the reservoir chamber is providedby a passage 78 and the passage 66 which both open into the bore 79 inwhich the valve assembly 61 is mounted.

The spring 77 is sized to provide a relatively light force urging thevalve disc 76 against the seat 74. Consequently, whenever the pressurein the passage 63 exceeds the pressure in the passage 78, and in turnthe pressure in the reservoir chamber 37, the disc is lifted away fromthe seat to allow flow. On the other hand, flow in the oppositedirection is positively prevented since the existence of pressure in thepassage 78 higher than in the passage 63 urges the disc toward itsseated position.

The valve assembly 61 functions to connect the reservoir chamber 37 withthe lower air motor chamber 43 only after a predetermined pressureexists in the cylinder 31. This is accomplished by providing a valvebody 81 which is threaded into the bore 79 and is pro vided with spacedseals 82 and 83 which provide a fluid tight joint with the bore atspaced locations. The portion inwardly of the body 81 is incommunication with the passage 63, and the portion intermediate theseals 82 and 83 is in communication with the passages 78 and 66.

An annular valve seat 84 is positioned in the valve body 81 and isengaged by a ball valve element 86. A spring 87 extends between the balland the adjusting screw 88 which is threaded into the body 81. The forceof the spring 87 on the ball 86 is varied by adjusting the screw 88inward or outward to either increase or de crease the force of thespring 87 on the ball. An operat ing plunger 89 is slidable in a bore 91and is provided with an extension 92 movable through the valve seat 84into engagement with the ball 86 to overcome the action of the spring 87and open the valve. The opposite end of the plunger 89 is incommunication with the pressure within the cylinder 31 through anannular groove 93 and radial ports 94. Spaced seals 96 are provided onthe plunger 89 on opposite sides of a port 97 which communicates withthe reservoir chamber 37. The port 97 cooperates with the spaced sealsto prevent any leakage of hydraulic fluid out of the cylinder 31 pastthe first seal 96 from reaching the valve section.

The effective area of the plunger 89 is greater than the effective areaof the ball 86. Consequently, even though the plunger 89 on the ball maybe exposed to the same pressures on opposite sides, the force developedby such pressure on the plunger is greater than the force developed onthe ball, and sufficient force will be developed to cause the plunger toslide to the right as viewed in FIGS. 1 and 2 and open the valve 61 whena predetermined pressure is reached in the cylinder bore 31corresponding to a given differential from the pressure in air space107. The value of such predetermined pressure can be adjusted byadjusting the force of the spring 87. A pressure gauge mounted on thehead 11 is connected through porting in the head to the pump chamber 48and indicates the hydraulic pressure developed.

The operation of the booster system can best be understood by referringto FIGS. 3 through 5. In these figures, work clamping devices areschematically illustrated at 101 and 102. Each of these devices is apiston and cylinder actuated type device having a piston 103 which isextended against the action of a spring 104 when hydraulic fluid underpressure is supplied thereto. The two clamping devices are connected inparallel to the outlet port 32 of the booster. FIG. 4, as previouslydiscussed, illustrates the connection of the booster through a four-wayvalve 54 to a compressor 56.

FIG. 3 illustrates the condition of the system before operation thereof.At this time, the pistons 103 are retracted by their associated springs104 and the reservoir chamber 37 is substantially filled with liquid 106leaving an air space 107 thereabove. When compressed air is supplied tothe air space 107 through the inlet port 52, it pressurizes the liquid106 and causes it to flow through the passages 51 into the hydraulicpump chamber 48. From there, the liquid under the pressure of thecompressed air passes to the clamping units 101 and 102 causing thepistons 103 to extend into engagement with the work piece to be clampedas schemati cally represented at 108. During this operation, the ballvalve 86 remains seated because the force of the spring 87 thereon issufficient to overcome the force of the plunger 89. After the work piece108 is engaged, a resistance to further flow is developed causing thepressure of the hydraulic fluid 106 to increase and approach thepressure of the compressed air supplied to the air space 107 by thecompressor 56.

The spring 87 is preferably adjusted so that when the pressure withinthe pump chamber 48 reaches a value of about 90 percent of the pressureof the supplied compressed air, a sufficient force is developed on theplunger 89 to cause it to move the ball valve 86 off of the seat. Forexample, if the pressure of the compressed air supplied to the system isin the order of 100 psi, the spring should be adjusted so that the ballvalve 86 is lifted away from its seat at about 90 psi.

As soon as the ball valve 86 is lifted away from its seat, the air motorchamber 43 is supplied with compressed air. At this time, the air motorchamber 44 above the piston head 41 is connected to exhaust by thefour-way valve 54 so the piston assembly starts to raise causing theplunger 42 to pass the passages 51 and isolate the pump chamber 48 fromthe reservoir chamber 37. Upward movement of the piston continues untila pressure is reached in the pump chamber 48 which is substantiallyequal to the supply compressed air pres sure times the ratio ofeffective area of the piston head 41 and plunger 42. In the illustratedembodiment, the area of the piston head 41 is about 30 times theeffective area of the plunger 42. Consequently, if the compressed air issupplied at a pressure in the order of 100 psi, the final operatingpressure of the hydraulic fluid will be approximately 3,000 psi. Theincrease in pressure will increase the clamping force of the clamps 101and 102 on the work piece 108. Because the pressure in the pumpingchamber 48 is higher at this time than the pressure of the compressedair supplied to the system, the plunger 89 maintains the ball valve inthe unseated position. During this phase of operation, the check valvedisc 76 remains closed, since the pressure thereacross is either higheron the spring side thereof or equal on both sides.

When it is desired to release the clamping force, the four-way valve 54is shifted to supply compressed air to the chamber 44 above the piston41 and the reservoir is connected to the exhaust 57. When this occurs,the piston 41 is driven downwardly to its retracted position asillustrated in FIG. 5. This causes a decrease in pressure and when theplunger 42 is retracted beyond the passages 51, communication isre-established between the reservoir chamber 37 and the pump chamber 48.Since the reservoir chamber is connected to exhaust at this time, thehydraulic pressure returns to atmospheric pressure. Consequently, thesprings 104 return the associated pistons 103 to the retracted positionreleasing the work piece. During the downward stroke of the piston, thedisc valve element 76 is lifted off of its seat so that the lower airmotor chamber 43 is exhausted even though the ball valve element 86reseats prior to full retraction of the piston.

Since the initial clamping is accomplished before the differentialpiston functions, it is not necessary to provide a large volumetriccapacity in the hydraulic pump even when a relatively large number ofclamping units is utilized. Further, all of the liquid 106 within thereservoir is available for the operation of the clamping devices, andnone of it is required for the operation of the air motor. With such asystem, the amount of compressed air required to operate the systemthrough a cycle of operation is relatively small. Further, the illustrated structure provides complete operation with only two very simplevalves which function with reliability and are low in cost.

Although a preferred embodiment of this invention is illustrated, it isto be understood that various modifications and rearrangements of partsmay be resorted without departing from the scope of the inventiondisclosed and claimed herein.

What is claimed is:

1. A hydraulic booster which cycles back-and-forth through a two-stagefeeding phase and a return-toreservoir phase comprising a pistonlessreservoir providing a lower portion adapted to receive hydraulic fluidwith an air space thereabove adapted to be supplied with compressed air,an air motor providing a piston defining a portion of an expansible airchamber, a hydraulic pump providing a plunger driven by said piston anddefining a part of an expansible hydraulic chamber connected at anoutput end to a hydraulic outlet port, said piston and plunger beingmovable between a retracted position and an extended position inresponse to compressed air supplied to said air chamber, the effectivearea of said piston being substantially larger than the effective areaof said plunger, flow con-' trol means connecting said lower portion tosaid hydraulic chamber when said piston is substantially in saidretracted position for feeding; of reservoir fluid in a first stage ofsaid feeding phase and isolating said lower portion and said hydraulicchamber in a second stage of said feeding phase when said piston ismoving from said retracted position toward said extended position, saidlast named connection being at an input end at the opposite end of saidhydraulic chamber from said output end, valved means exhausting said airchamber when said air space is exhausted and maintaining said airchamber and air space at substantially the same pressure when thepressure in said hydraulic chamber exceeds a predetermined differencefrom the pressure in said air space, and means for self-purging of airfrom said booster upon back-and-forth cycling of said booster, saidmeans including direct interfacing between the hydraulic fluid and theair space in said reservoir and the constituting of said hydraulicchamber as an elongate and relatively narrow passageway within whichsubstantially all points are on-line with respect to fluid flow betweensaid output end connection and said input end connection.

2. A hydraulic booster as set forth in claim 1 wherein said plungercloses said flow control means and isolates said hydraulic chamberexcept when said plunger is in said retracted position.

3. A hydraulic booster as set forth in claim 2 wherein said valved meansincludes a valve member, and a mov able surface exposed to pressure insaid hydraulic chamber operable to move said valve member to an openposition when such pressure reaches said prede termined pressuredifference.

4. A hydraulic booster as set forth in claim 3 wherein said valved meansincludes adjustable spring means operable to adjust said predeterminedpressure difference.

5. A hydraulic booster as set forth in claim 4 wherein said booster isoperated by a supply pressure, and said predetermined pressure isadjusted according to said supply pressure.

6. A hydraulic booster as set forth in claim 5 wherein said valved meansconnects said air space and said air chamber.

7. A hydraulic booster as set forth in claim 6 wherein said valved meansprovides a check valve in'parallel with said valve member.

8. A hydraulic booster as set forth in claim 1 wherein said valved meansconnects said air space and said air chamber 9. A hydraulic booster asset forth in claim 1 wherein said piston is double-acting.

10. A pressure multiplying apparatus which cycles back-and-forth througha two-stage feeding phase and a returnto-reservoir phase comprising apistonless fluid tight reservoir containing liquid with an air spacethereabove adapted to receive air under pressure, a differential areapump means having a piston reciprocable between a retracted and anextended position, said piston having a first surface defining part ofan expansible air chamber and a second surface substantially smallerthan said first surface defining a part of an expansible liquid chamberconnected at an output end to a liquid outlet port, passage meansconnecting the liquid in said reservoir to said liquid chamber forfeeding of reservoir fluid in a first stage of said feeding phase onlywhen said piston is in said retracted position, said last namedconnecting being at an input end at the opposite end of said liquidchamber from said output end, valve means connecting said air chamberand said air space when the pressure in said air chamber exceeds thepressure in said air space and when the pressure in said liquid chamberexceeds a predetermined difference from the pressure in said air space,means for adjusting said predetermined difference, air pressure in saidair chamber operating to move said piston from said retracted positiontoward an extended position in a second stage of said feeding phase andpressurizing the liquid in said liquid chamber to a pressuresubstantially higher than said air pressure, said piston remaining insaid retracted position when air under pressure is supplied to said airspace until the pressure in said liquid chamber reaches saidpredetermined difference of pressure and thereafter moving toward saidextended position and pressurizing the liquid in said liquid chamber toa pressure substantially higher. than the pressure of air supplied tosaid air space, and means for self-purging of air from said apparatusupon back-and-forth cycling of said apparatus, said means includingdirect interfacing between the hydraulic fluid and the air space in saidreservoir and the constituting of said liquid chamber as an elongate andrelatively narrow passageway within which substantially all points areon-line with respect to fluid flow between said output end connectionand said input end connection.

11. A hydraulic booster which cycles back-and-fo'rth through a two-stagefeeding phase and a return to reservoir phase comprising a housingassembly provided with a partition separating said assembly into an aircylinder portion on one side of said partition and a hydraulic reservoirportion on the other side of said partition, the hydraulic reservoirdefined by said hydraulic reservoir portion being pistonless, ahydraulic cylinder in said housing defining a separate pump chamberconnected at an output end to a liquid output port, differential areapump means including a piston reciprocable in said air cylinder and aplunger reciprocable in said pump chamber, said piston defining a partof an air chamber, pressure in said air chamber causing movement of saidpump means from a retracted position toward an extended position,passage means connecting the lower portion of said reservoir and saidpump chamber for feeding of reservoir fluid in a first stage of saidfeeding phase only when said pump meansis in said retracted position,said last named connection being at an input end at the opposite end ofsaid pump chamber from said output end, movement of said pump means fromsaid retracted position toward said extended position in a second stageof said feeding phase causing closing of said passage means andisolation of said pump chamber from said reservoir, and valved meansconnecting the upper portion of said reservoir and said air chamber whenthe pressure in said pump chamber exceeds a predetermined differencefrom the pressure in said air space, and means for self-purging of airfrom said booster upon back-and-forth cycling of said booster, saidmeans including direct interfacing between the hydraulic fluid and theair space in said reservoir and the constituting of said pump chamber asan elongate and relatively narrow passageway within which substantiallyall points are on-line with respect to fluid flow between said outputend connection and said input end connection.

12. A hydraulic booster as set forth in claim 11 wherein said housing isgenerally cylindrical and said partition extends laterally thereacross,said reservoir being located above said partition and said air cylinderbeing located below said partition. I

13. A hydraulic booster as set forth in claim 12 wherein said hydrauliccylinder extends axially along the interior or said reservoir.

1. A hydraulic booster which cycles back-and-forth through a two-stagefeeding phase and a return-to-reservoir phase comprising a pistonlessreservoir providing a lower portion adapted to receive hydraulic fluidwith an air space thereabove adapted to be supplied with compressed air,an air motor providing a piston defining a portion of an expansible airchamber, a hydraulic pump providing a plunger driven by said piston anddefining a part of an expansible hydraulic chamber connected at anoutput end to a hydraulic outlet port, said piston and plunger beingmovable between a retracted position and an extended position inresponse to compressed air supplied to said air chamber, the effectivearea of said piston being substantially larger than the effective areaof said plunger, flow control means connecting said lower portion tosaid hydraulic chamber when said piston is substantially in saidretracted position for feeding of reservoir fluid in a first stage ofsaid feeding phase and isolating said lower portion and said hydraulicchamber in a second stage of said feeding phase when said piston ismoving from said retracted position toward said extended position, saidlast named connection being at an input end at the opposite end of saidhydraulic chamber from said output end, valved means exhausting said airchamber when said air space is exhausted and maintaining said airchamber and air space at substantially the same pressure when thepressure in said hydraulic chamber exceeds a predetermined differencefrom the pressure in said air space, and means for self-purging of airfrom said booster upon back-and-forth cycling of said booster, saidmeans including direct interfacing between the hydraulic fluid and theair space in said reservoir and the constituting of said hydraulicchamber as an elongate and relatively narrow passageway within whichsubstantially all points are on1line with respect to fluid flow betweensaid output end connection and said input end connection.
 2. A hydraulicbooster as set forth in claim 1 wherein said plunger closes said flowcontrol means and isolates said hydraulic chamber except when saidplunger is in said retracted position.
 3. A hydraulic booster as setforth in claim 2 wherein said valved means includes a valve member, anda movable surface exposed to pressure in said hydraulic chamber operableto move said valve member to an open position when such pressure reachessaid predetermined pressure difference.
 4. A hydraulic booster as setforth in claim 3 wherein said valved means includes adjustable springmeans operable to adjust said predetermined pressure difference.
 5. Ahydraulic booster as set forth in claim 4 wherein said booster isoperated by a supply pressure, and said predetermined pressure isadjusted according to said supply pressure.
 6. A hydraulic booster asset forth in claim 5 wherein said valved means connects said air spaceand said air chamber.
 7. A hydraulic booster as set forth in claim 6wherein said valved means provides a check valve in parallel with saidvalve member.
 8. A hydraulic booster as set forth in claim 1 whereinsaid valved means connects said air space and said air chamber
 9. Ahydraulic booster as set forth in claim 1 wherein said piston isdouble-acting.
 10. A pressure multiplying apparatus which cyclesback-and-forth through a two-stage feeding phase and areturn-to-reservoir phase comprising a pistonless fluid tight reservoircontaining liquid with an air space thereabove adapted to receive airunder pressure, a differential area pump means having a pistonreciprocable between a retracted and an extended position, said pistonhaving a first surface defining part of an expansible air chamber and asecond surface substantially smaller than said first surface defining apart of an expansible liquid chamber connected at an output end to aliquid outlet port, passage means connecting the liquid in saidreservoir to said liquid chamber for feeding of reservoir fluid in afirst stage of said feeding phase only when said piston is in saidretracted position, said last named connecting being at an input end atthe opposite end of said liquid chamber from said output end, valvemeans connecting said air chamber and said air space when the pressurein said air chamber exceeds the pressure in said air space and when thepressure in said liquid chamber exceeds a predetermined difference fromthe pressure in said air space, means for adjusting said predetermineddifference, air pressure in said air chamber operating to move saidpiston from said retracted position toward an extended position in asecond stage of said feeding phase and pressurizing the liquid in saidliquid chamber to a pressure substantially higher than said airpressure, said piston remaining in said retracted position when airunder pressure is supplied to said air space until the pressure In saidliquid chamber reaches said predetermined difference of pressure andthereafter moving toward said extended position and pressurizing theliquid in said liquid chamber to a pressure substantially higher thanthe pressure of air supplied to said air space, and means forself-purging of air from said apparatus upon back-and-forth cycling ofsaid apparatus, said means including direct interfacing between thehydraulic fluid and the air space in said reservoir and the constitutingof said liquid chamber as an elongate and relatively narrow passagewaywithin which substantially all points are on-line with respect to fluidflow between said output end connection and said input end connection.11. A hydraulic booster which cycles back-and-forth through a two-stagefeeding phase and a return to reservoir phase comprising a housingassembly provided with a partition separating said assembly into an aircylinder portion on one side of said partition and a hydraulic reservoirportion on the other side of said partition, the hydraulic reservoirdefined by said hydraulic reservoir portion being pistonless, ahydraulic cylinder in said housing defining a separate pump chamberconnected at an output end to a liquid output port, differential areapump means including a piston reciprocable in said air cylinder and aplunger reciprocable in said pump chamber, said piston defining a partof an air chamber, pressure in said air chamber causing movement of saidpump means from a retracted position toward an extended position,passage means connecting the lower portion of said reservoir and saidpump chamber for feeding of reservoir fluid in a first stage of saidfeeding phase only when said pump means is in said retracted position,said last named connection being at an input end at the opposite end ofsaid pump chamber from said output end, movement of said pump means fromsaid retracted position toward said extended position in a second stageof said feeding phase causing closing of said passage means andisolation of said pump chamber from said reservoir, and valved meansconnecting the upper portion of said reservoir and said air chamber whenthe pressure in said pump chamber exceeds a predetermined differencefrom the pressure in said air space, and means for self-purging of airfrom said booster upon back-and-forth cycling of said booster, saidmeans including direct interfacing between the hydraulic fluid and theair space in said reservoir and the constituting of said pump chamber asan elongate and relatively narrow passageway within which substantiallyall points are on-line with respect to fluid flow between said outputend connection and said input end connection.
 12. A hydraulic booster asset forth in claim 11 wherein said housing is generally cylindrical andsaid partition extends laterally thereacross, said reservoir beinglocated above said partition and said air cylinder being located belowsaid partition.
 13. A hydraulic booster as set forth in claim 12 whereinsaid hydraulic cylinder extends axially along the interior or saidreservoir.